1. Field of the Invention
The present invention relates to a capacitive type ultrasonic transducer, a fabrication method for the ultrasonic transducer, and an ultrasonic endoscope which has the ultrasonic transducer in an ultrasonic transmission and reception portion.
2. Description of the Related Art
To form cavities in an ultrasonic transducer, a method is known which creates cavities and channels communicating the cavities with each other by using a sacrificial layer, forms an insulating layer on the sacrificial layer, creates holes in the insulating layer, pours a chemical agent or gas to dissolve the sacrificial layer, and thereby removes the sacrificial layer. This method can form cavities under the insulating layer. Besides, it is necessary to form sealing portions to prevent holes for subsequent processes. With conventional techniques, however, material used to form the sealing portions is deposited in the cavities more than necessary, distorting shape of the sealing portions. This makes shape of the cavities non-uniform.
U.S. Pat. No. 5,982,709A discloses a fabrication technique for an ultrasonic transducer in which channels for removal of a sacrificial layer are formed in membrane support posts along a substrate surface. The ultrasonic transducer can avoid deposition of film-forming member in cavities during a CVD (Chemical Vapor Deposition) based film formation process for forming sealing portions intended to plug sacrificial layer removal holes made in the membrane support posts and can prevent vibration of membranes from being hindered.
That is, the ultrasonic transducer disclosed in U.S. Pat. No. 5,982,709A prevents the film-forming member from entering the cavities using a crank-shaped (T-shaped) geometry for the channels running from the sealing portions to the cavities, where the sealing portions are created by forming a film in the sacrificial layer removal holes by CVD.